This invention relates to a process for protection against the non-authorized inhibition of writing in certain storage areas of a smart card, and device for the use of the process.
In a pay-television network whereby the decoders are equipped with smart cards, when the card reaches the end of the period of validity or when it recognizes the need to inhibit definitively forged cards (which all have the same identity due to identical forging), the emitter sends a signal ordering end-of-validity data, or data inhibiting further access, to be entered into these cards. The writing signal used for this card operation appears on a given conductor within the decoder and is easily identified by a person wishing to pirate the card (generally, this conductor has a higher voltage than the card supply voltage). The simple action of cutting this conductor prevents the card from being invalidated.
A solution which is well-known in the art, recommended by the current Eurocrypt standard, consists in reserving in the area of card storage a zone in which the dates indicating the beginning and end of the validity period are written, a program ordering self-destruction of the card when the end of the period of validity has been reached (the emitter constantly indicates the current date to the card). However, memorizing this type of data in the card results in a considerable decrease in storage capacity, and in the data transmission capacity of the network.
The object of this invention is a process, straightforward and easy to apply, for the protection against the non-authorized inhibition of writing in certain storage areas of a smart card used in a network consisting of at least one management center or emitter, and at least one terminal or receiver equipped with the means to operate with smart cards.
A further object of this invention is a simple device for the use of the process.